This invention relates to a method and an apparatus for decontaminating fluids. More particularly, this invention relates to a method and an apparatus for decontaminating fluids, particularly wastewater, using variable-pulsed ultraviolet (UV) radiation.
The availability of inexpensive, usable water has greatly diminished over this century, and stress upon water resources is expected to increase dramatically with accelerating population and pollution. Throughout the world, industry and governments are increasingly confronted with the challenge and expense of providing modem wastewater facilities that meet public demand and enacting stringent regulatory requirements necessary to produce a cleaner environment. Globally, the need for economic, environmentally friendly industrial wastewater treatment is rapidly approaching a crisis point.
Wastewater (including industrial and municipal wastewater) frequently contains contaminants such as, e.g., microorganisms and toxic organic compounds, which may prove to be toxic in subsequent uses of the water. Examples of microorganisms frequently found in wastewater include bacteria, spores, yeasts, or fungi, algae, etc., including viruses or bacteriophages. Toxic organic compounds found in wastewater include, e.g., cancer-causing aromatic compounds and numerous halogen compounds, particularly chlorine compounds, e.g., chlorinated phenols, etc.
There are many known techniques for disinfecting wastewater, including the use of chemical or physical agents, mechanical means, and UV radiation. Of these, the traditional method of disinfection has been the use of chemical agents in the form of chlorine. Although chlorine disinfection has significantly reduced the incidence of water-borne disease in the United States for many years, growing concerns about chlorine's safety and effect on the environment have prompted wastewater treatment utilities to evaluate other disinfection methods.
To date, the most viable alternative to chlorine disinfection is ultraviolet (UV) disinfection.
Chemical bonds in organic toxins can be broken under the action of the UV radiation through photodissociation. A particular substance will have a characteristic photodissociation curve associated with it specifying the energies and wavelengths of UV radiation for which the particular substance will undergo photodissociation. For effective photodissociation, it is necessary that the UV radiation have the particular energy or energies which fall within the photodissociation curve of the substance of interest.
With respect to microorganisms, disinfection occurs when UV light contacts the microorganism's deoxyribonucleic acid (DNA) molecules, which contain the genetic information necessary for cell replication. The light causes double bonds to form between adjacent subgroups in the DNA structure, preventing normal replication of DNA molecules and thereby inactivating the microorganism.
It is also known that pulsed UV flashlamps can produce a high-power output that is effective for various photodissociation applications, including the disinfection and purification of fluids.
The use of ultraviolet radiation to destroy microorganisms and/or effect photodissociation of organic compounds in wastewater is disclosed, e.g., in U.S. Pat. Nos. 4,661,264 and 4,816,145 (both to Goudy, Jr.); 5,144,146 (Wekhof); 4,400,270 and 4,336,223 (both to Hillman); 5,368,826 (Weltz, et al.); 4,464,336 (Hiramoto); 5,230,792 (Sauska et al.); 5,547,590 (Szabo); 5,900,211 (Dunn et al.); 1,670,217 (Scheidt); 2,338,388 (Whitman); 4,769,131 (Noll et al.); 5,504,335 (Maarschalkerweerd); 4,296,066 and 4,317,041 (both to Schenck); 5,768,853 (Bushnell et al.); 5,597,482 (Melyon); 5,322,569 (Titus et al.); 5,536,395 (Kuennen et al.); 5,915,161 (Adams); 5,208,461 (Tipton); 5,364,645 (Lagunas-Solar et al.); 5,925,885 (Clark et al.); 5,503,800 (Free); 3,485,576 (McRae et al.); 3,814,680 (Wood); 3,637,342 (Veloz); 3,924,139; 4,103,167 and 4,767,932 (both to Ellner); 4,204,956 (Flatow); 4,471,225 (Hillman); 4,621,195 (Larrson); 4,676,896 (Norton); 4,909,931 (Bibi); 5,624,573 (Wiesman); 5,626,768 (Ressler et al.); 5,660,719 (Kurtz et al.); 5,725,757 (Binot); 5,738,780 (Markham); 4,757,205 (Latel et al); 5,290,439 (Buchwald); 5,925,240 (Wilkins, et al.); 4,880,512 (Cornelius et al;); 4,246,101 (Selby, III); 5,151,252 (Mass); 4,274,970 (Beitzel); 4,230,571 (Dadd); 4,304,996 (Blades); and 5,480,562 (Lemelson). See also Legan, R.W., Ultraviolet Light Takes on CPI Role, Chemical Engineering, pp. 95-100 Jan. 22, 1982).
Another article of interest is Hanzon, B. D. and Vigilia, Rudy, Just the Facts: UV Disinfection, Water Environment & Technology Magazine (Nov. 1999), which is hereby incorporated by reference herein.
In many commercial applications, it is highly desirable to deliver UV radiation to a target in a manner that simultaneously produces excellent process efficacy, economic efficiency, and the ability to do so at all times at all required fluid flow rates. Too high a UV dosage can become an unacceptable economic burden, but an insufficient UV dosage can be dangerous.
An ideal UV-based water-disinfection system has a number of advantageous characteristics.
For example, an ideal UV-based disinfection system can provide exact application of the desired UV dosage at all times (in real time) instead of sometimes or much of the time, regardless of the influent's UV transmission level or variances in the influent's pressure or flow rate.
Furthermore, an ideal UV-based water-disinfection system further can confirm the integrity of the operational parameters. For example, the system provides active, real-time control feedback regarding the UV lamp's baseline output level and the influent's UV tansmissivity and flow rate. The system also provides a dynamic and wide-range, real-time response for adjusting the UV light power output and influent flow rate in response to such feedback.
An ideal UV disinfection system also has automatic compensative adaptability to any degradation in one or more UV reactor sections used in the system such that the system provides an active, real-time response to such degradation and assures process integrity, e.g., by not passing non-conforming effluent.
Various UV disinfection systems have been developed in an attempt to provide improved control over the dose parameters. Such systems are disclosed, e.g., in U.S. Pat. Nos. 4,317,041; 4,336,223; 5,144,146; 5,208,461; 5,364,645; 5,547,590; and 5,925,885. However, such conventional systems generally do not have all of the desired characteristics discussed hereinabove in connection with an ideal UV disinfection system. The drawbacks to such systems can be broken down into one or more of the areas discussed below.
For example, one drawback to the conventional UV disinfection systems is their use of continuous wave lamps. Most continuous wave lamps require a warn-up period prior to operation. In addition, most continuous wave lamps are adversely affected by frequent "on-off" cycling, experience excessive jacket fouling, and do not operate efficiently over a wide range of power output.
In another drawback, conventional UV disinfection systems use UV lamps arranged in large banks that constitute a single reactor. With such arrangement of the lamps constituting a single reactor, wide and random variations in UV intensity among the individual lamps can considerably vary the dosage delivered across sections within such reactor. More importantly, accurate monitoring of each lamp's baseline output performance is impractical because every lamp would require a separate UV detector. Therefore, the UV output (and subsequently the performance) of such reactor can only be estimated via discrete probe points that do not necessarily represent anything more than a small section of the reactor. Individual lamp performance is unknown.
A further drawback to the conventional UV disinfection systems is the use of passive flow control devices (e.g., weirs, gate, valves and the like) and gravity flow. As a result, the practical operating ranges of such systems work to restrict the available flow ranges of the reactors used therein. Hydraulic head losses quickly dominate the design equations, thereby limiting reactor performance range. Flow adjustments are relatively slow to execute, and a flow change in any one reactor can adversely create a flow change in adjacent reactors.
Because of the drawbacks discussed above, the conventional disinfection systems are not truly active, real-time or independent, but instead are dependent upon slower, passive techniques for monitoring and adjusting performance parameters. These systems typically exhibit large interaction dependencies among the multiple reactors that constitute an industrial-capacity system. Accurate UV dosage is compromised, along with the ability of the system to adjust parameters as needed for optimized efficiency.
The needs of the water and wastewater disinfection industry for higher system efficiency and lower total cost of operation increasingly necessitates advances beyond those of conventional UV disinfection systems.
Accordingly, a primary object of the present invention is to provide a reliable and cost-effective system (i.e., method and apparatus) for chemical-free decontamination of water (including wastewater).
A further object of this invention is to provide a UV-based decontamination system which has the capability to instantly adjust the output power of the UV reactors over a wide range, thereby instantly adjusting the UV dosage when required.
Another object of this invention is to provide a UV-based decontamination system which uses a single UV light source in each UV reactor, whereby the performance of the single UV light source consistently and accurately represents the performance of the entire reactor.
A still further object of this invention is to provide a UV-based decontamination system wherein, in each UV reactor, the baseline UV light output from the UV light source can be accurately determined at any given instant, as can the actual UV transmission within the reactor.
Yet another object of this invention is to provide a UV-based decontamination system wherein each UV reactor is capable of controlling the influent flow rate within that reactor, can instantly achieve upon command a very wide and precise range of operation, and exhibits zero hydraulic head loss, further wherein each UV reactor is capable of doing the foregoing independently of and without interaction with the other UV reactors within the system.
Another object of this invention is to provide a UV-based decontamination system which has monitoring and control feedback means that can provide an active, real-time response for system parametric optimization, and can do so with complete independence among the UV reactors constituting the system.
A further object of this invention is to provide a UV-based decontamination system capable of accurate and fail-safe optimization of UV dose throughout the entire range of operating conditions that are typically encountered in large-scale UV photodissociation applications.
These and other objects are achieved in the present invention.